1. Field of the Invention
The present invention relates to the field of digital and analogue information transmission; and, more particularly, to a filter circuit having an Fe-based amorphous metal core, for bandpass filtering in telecommunication applications, such as DSL communications circuits, and the like.
2. Description of the Prior Art
Telephone communication lines are presently used to produce a wide variety of signals for both commercial and domestic users of a product or service. Such a product or service, of course, includes normal voice telephone and communications, as well as a growing number of ancillary services. Ancillary services are generally directed towards the transmission of information over existing telephone lines. This information presently includes computer data, i.e., transmitted over two-way Internet connections, as well as a growing number of other ancillary services. Those further ancillary services which are currently under development, or contemplated, include one-way and two-way continuous broadcast information, such as audio only (radio), video streams, mixed audio/video streams, and the like.
The foregoing modes of communication are made possible by existing telephone lines, which provide a network capable of carrying a broad range of this information. While available bandwidths generally range from about 0 to 3000 kHz, the actual bandwidth requirements for conventional voice-only telecommunications is in the neighborhood of up to about 6 kHz. Thus, there exists the potential for the use of this existing network to transmit communications at higher frequencies.
The technique of providing information within a certain range of frequencies, i.e., a limited “bandwidth” enables the simultaneous transmission of different signals along a single circuit. This eliminates the need for multiple circuits wherein the signal being transmitted along communication lines can be maintained within separate frames of frequencies, i.e., separate bandwidths within the available frequency spectrum for a circuit. Conventionally, this has been accomplished by use of a “bandpass filter”, which typically include a coil and a capacitor. The operating characteristics of the coil and capacitor are selected such that only a limited subset of the total available frequency spectrum passes through the communication lines. Bandpass filters are typically placed between the source of communications and the communication lines, thereby limiting the output of the communications device to fall solely within the frequency range established for the particularly bandpass filter. A plurality of bandpass filters, each having outputs of non-overlapping frequency ranges within an available spectrum can also be used, and thus a plurality of communication devices can share common communication lines.
In the past, choke coils have been used in telecommunication circuits. While advantageous, the use is not without shortcomings. Such shortcomings include incompatibility of controlling desired choke coil performance needed for pertinent use such as in band pass filter circuits. These shortcomings have created a need for materials having “softer” and more controllable magnetic properties. In certain cases cobalt containing amorphous metal alloys have been used to form choke coil cores. Although more prevalent and less expensive, iron-rich amorphous metal cores have not been used in choke coil cores, since their inductance properties were believed unsuitable for use in bandpass filters.